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add lua DSP transfer function calculation

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This commit is contained in:
Robin Gareus 2016-05-20 23:14:51 +02:00
parent 125e2014aa
commit d7e590f9c8
3 changed files with 36 additions and 3 deletions
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7
libs/ardour/ardour/dsp_filter.h
View file

@ -228,6 +228,13 @@ namespace ARDOUR { namespace DSP {
* @param gain filter gain
*/
void compute (Type t, double freq, double Q, double gain);
/** filter transfer function (for spectrum visualization)
* @param freq frequency
* @return gain at given frequency in dB
*/
float dB_at_freq (float freq) const;
/** reset filter state */
void reset () { _z1 = _z2 = 0.0; }
private:

31
libs/ardour/dsp_filter.cc
View file

@ -145,14 +145,18 @@ BiQuad::run (float *data, const uint32_t n_samples)
void
BiQuad::compute (Type type, double freq, double Q, double gain)
{
if (Q <= .001) { Q = 0.001; }
if (freq <= 1.) { freq = 1.; }
if (freq >= _rate) { freq = _rate; }
/* Compute biquad filter settings.
* Based on 'Cookbook formulae for audio EQ biquad filter coefficents'
* by Robert Bristow-Johnson
*/
const double A = pow (10.0, (gain / 40.0));
const double A = pow (10.0, (gain / 40.0));
const double W0 = (2.0 * M_PI * freq) / _rate;
const double sinW0 = sin (W0);
const double cosW0 = cos (W0);
const double sinW0 = sin (W0);
const double cosW0 = cos (W0);
const double alpha = sinW0 / (2.0 * Q);
const double beta = sqrt (A) / Q;
@ -250,3 +254,24 @@ BiQuad::compute (Type type, double freq, double Q, double gain)
_a1 /= _a0;
_a2 /= _a0;
}
float
BiQuad::dB_at_freq (float freq) const
{
const double W0 = (2.0 * M_PI * freq) / _rate;
const float c1 = cosf (W0);
const float s1 = sinf (W0);
const float A = _b0 + _b2;
const float B = _b0 - _b2;
const float C = 1.0 + _a2;
const float D = 1.0 - _a2;
const float a = A * c1 + _b1;
const float b = B * s1;
const float c = C * c1 + _a1;
const float d = D * s1;
#define SQUARE(x) ( (x) * (x) )
return 20.f * log10f (sqrtf ((SQUARE(a) + SQUARE(b)) * (SQUARE(c) + SQUARE(d))) / (SQUARE(c) + SQUARE(d)));
}

1
libs/ardour/luabindings.cc
View file

@ -1166,6 +1166,7 @@ LuaBindings::dsp (lua_State* L)
.addFunction ("run", &DSP::BiQuad::run)
.addFunction ("compute", &DSP::BiQuad::compute)
.addFunction ("reset", &DSP::BiQuad::reset)
.addFunction ("dB_at_freq", &DSP::BiQuad::dB_at_freq)
.endClass ()
/* DSP enums */